The present disclosure herein relates to a planar waveguide, and more particularly, to an optical mode size conversion technique of a planar waveguide.
When an end of a planar optical waveguide is optically connected to an end of an optical fiber or another planar optical waveguide, an optical mode size conversion technique of the optical waveguide is required to minimize an optical power loss.
As an example of the optical mode size conversion technique, there is a method of converting an optical mode size by gradually reducing a width of a core in an optical mode size conversion region. However, in this technique, the optical mode size may significantly increases as the width of the core decreases. In this case, when the optical waveguide is manufactured, it may be difficult to precisely control the width of the core at an end of the optical waveguide so as to approach a design value.
As another example of the optical mode size conversion technique, there is a method of converting the optical mode size by using a segmented core structure one-dimensionally arranged in the optical mode size conversion region. This technique has three design variables (a width and a length of each of segmented cores and a distance between the segmented cores), but it is difficult to derive a satisfactory design in terms of an optical mode size and shape.